Cast Steel* 
407 
finally digested for a minute in weak ammonia, should be 
heated in a flask almost to redness, to expel the water and 
any muriat of ammonia that it may contain ; being then 
weighed, it is to be ignited in a silver or platina crucible 
till the whole of the carbon is burnt off, and the residual 
iron is oxydized : from the weight of this o: yd is to be 
deducted 48 per cent, on account of the oxygen, and the 
difference between the weight of the remainder and that of 
the black powder before ignition indicates the amount of 
carbon. 
The affinity of iron for carbon is pretty considerable, 
though it is by no means capable of decomposing car- 
bonic acid by combining with its base, as Mushet has 
clearly shown in opposition to the assertion of Clouet. 
The effects produced upon iron by carbon are very 
remarkable. First with regard to colour : the blueish grey 
tint of iron becomes more and more white in proportion 
as it combines with carbon, till it possesses almost a silve* 
ry colour and lustre, as is the case with the white cast iron 
in which state the metal seems to be saturated with car- 
bon. At the same time that these changes of colour 
are going on, the tendency to crystallization is rapidly in- 
creasing, hence the fracture from being fibrous and hack- 
ly, becomes first compact, then granular, and at length ex- 
hibits facets like antimony. W ith these changes the fusi- 
bility increases, and the faculty of welding diminishes, and 
soon entirely ceases : the ductility and malleability also 
undergo an analogous change, though not quite to so 
great an extent : the hardness increases, as also does the 
property of induration by sudden cooling, and the capabi- 
lity of being tempered* 
Iron however may not only be saturated but supersa- 
turated with carbon : that is to say, when at a very high 
temperature it will dissolve more carbon than it can hold 
in solution at a lower temperature ; and in consequence, 
